1. Field of the Invention
This invention pertains to the bag making art and more particularly relates to an apparatus for stripping the web from the sealing heads of a bag machine or the like.
2. Description of Prior Art
In the thermosealing or thermoplastic bag making industry, bag producers frequently desire to make bags from tubular stock with their closed ends first or downstream relative to the direction of movement of the web. These bags are known as bottom weld, closed end first bags. Since the thermosealing operation melts or partially melts the bag material, there is a tendency for the hot material at the forward end of the web to adhere to one or both of the sealing heads. Thus, steps must be taken to strip the web from both seal bars or heads since the web is usually quite thin and, if adhered to one of the heads, cannot be pushed, as opposed to being pulled, through the sealing and severing station by the intermittent web advancing draw rolls.
U.S. Pat. No. 3,813,998 which issued to Ronald L. Lotto on June 4, 1974 and is assigned to the assignee of the present invention discloses one way of stripping film from the seal bars. In the Lotto machine, as well as in the subject bag machine, the drive means for the draw rolls includes a portion which oscillates thereby driving the draw rolls from about zero velocity through a maximum velocity and back to about zero velocity during each forward or draw stroke of the draw rolls. In order to strip the web in the Lotto bag machine, the drive to the draw rolls is clutched in early so that the draw rolls will rotate at a very slow speed in a reverse direction about 10.degree. thereby gently pulling the web rearwardly to positively strip it from the weld bars prior to driving the rolls forwardly to gradually accelerate and thereafter decelerate the web while advancing the web one bag length through the sealing and severing station.
U.S. Pat. No. 2,882,956 which issued to Weist on Nov. 9, 1956 likewise discloses a bag machine which pulls the web free from a seal bar in a reverse direction but does not gradually accelerate and decelerate the web.